Hydromechanical lead-lag control device

ABSTRACT

A fluid reaction device for generating a lead-lag function to stabilize a fluid servoloop, which device employs two different area spools or pistons mounted on a single spindle or rod with suitable biasing. A small piston is mounted in a corresponding cylinder and has a rigidly carrying rod drivingly connected to a mechanical control linkage. The rod is freely surrounded by an annular larger piston carried within a correspondingly larger cylinder adjacent the smaller cylinder. A first expansible chamber is thus formed on the side of the larger piston opposite from the smaller piston and a second expansible chamber is formed between the pistons. Variable pressure feed-back fluid is fed into the first expansible chamber and discharged from an outlet port, which may be partially blocked by the larger piston so that fluctuations in the incoming fluid pressure will produce corresponding axial movement fluctuations of the larger piston, which in turn will produce corresponding axial fluctuations in the movement of the smaller piston in a ratio of their areas due to the driving effect of the fluid within the second substantially closed expansible chamber. Bleed passages are provided from the second expansible chamber in the pistons for reducing the ratio of movement between the pistons for low frequency fluctuations of the inlet pressure, as compared to a higher ratio of movement for high frequency fluctuations. Particularly, the device is well suited for use as a feed-back control in the throttle linkage of an internal combustion engine wherein the fluid fed to the first expansible chamber fluctuates in flow in correspondence with engine speed.

United States Patent Honda 1 Aug. 22, 1972 HYDROMECHANICAL LEAD-LAG piston is mounted in a corresponding cylinder and has CONTROL DEVICE a rigidly carrying rod drivingly connected to a [72] Inventor: Thomas Shaw Honda, Scottia, N.Y. mechamcal control lmkage' h rod freely rounded by an annular larger p1ston carried w1th1n a [73] AS igne I General Elec ri Company correspondingly larger cylinder adjacent the smaller [22] Filed: Nov. 27, 1970 cylinder. A first expansible chamber is thus formed on the side of the larger piston opposite from the smaller PP 93,106 piston and a second expansible chamber is formed between the pistons. Variable pressure feed-back fluid 52 US. c1 123/108, /52 SR, 91/47, is fed the first eXPatSib'e chamber and discharged 92/65 123/140 R from an outlet port, which may be partially blocked by 51 1m. (:1 ..F02d 9/00 the larger P so that fluctuations in the incoming [58] Field of Search ..92/; 91/47; 60/52 SR; fluid Pressure will Produce Corresponding axial move- 123/m8, R, 140 J 140 p ment fluctuations of the larger piston, which in turn will produce corresponding axial fluctuations in the [56] References Cited movement of the smaller piston in a ratio 'of their areas due to the driving effectof the fluid within the FOREIGN PATENTS OR APPLIC IO second substantially closed expansible chamber. Bleed 132,604 8/1951 Sweden ..60/52 SR Passages Provicled mm the Sectmd expansible Primary Examiner-Wendell E. Burns Att0rney-Frank L. Neuhauser, Oscar B. Waddell, Joseph B. Forman and Francis K. Richwine 57 ABSTRACT A fluid reaction device for generating a lead-lag function to stabilize a fluid servoloop, which device employs two different area spools or pistons mounted on a single spindle or rod with suitable biasing. A small chamber in the pistons for reducing the ratio of movement between the pistons for low frequency fluctuations of the inlet pressure, as compared to a higher ratio of movement for high frequency fluctuations. Particularly, the device is well suited for use as a feedback control in the throttle linkage of an internal combustion engine wherein the fluid fed to the first expansible chamber fluctuates in flow in correspondence with engine speed.

11 Claims, 3 Drawing Figures t. W 38 3/? l as 36 i I. I g7///////////A M 22 -vo 7; u

Patented Aug. 22, 1972 3,685,501

3 Sheets-Sheet 1 INVENTOR THOMAS S.HONDA IS ATTORNEY Patented Aug. 22, 1972 3 Sheets-Sheet 5 INVENTOR THOMAS S, HONDA H S ATTORNEY I-IYDROMECI-IANICAL LEAD-LAG CONTROL DEVICE BACKGROUND OF THE INVENTION tion and inertia of such linkages considerably decrease lo their effectiveness, particularly with respect to high frequency operation. This friction problem is compounded by the very close tolerance machining of the linkage, all of which contributes to early failure. In general these linkages have proved very trouble some.

Particularly, there is a considerable need to stabilize a hydromechanical speed control loop without the above-mentioned disadvantages of known mechanical linkages. The patent to Lewis et al., US. Pat. No. 3,324,740, issued June 13, 1967, to the assignee of the present invention, is an example of a prior art power system control that employs a lead-lag unit for stabilizing a hydromechanical servoloop, which unit has many of the disadvantages mentioned above due to its mechanical linkage. There are many other fields of art that require stabilizing units with a lead-lag function, for example, in the control of heavy machine tools and in assembly line equipment for various manufacturing facilities.

SUMMARY OF THE INVENTION The present invention has as an object to overcome the disadvantages of the prior art while satisfying the needs of the prior art, as mentioned above. Particularly, it is an object of the present invention to provide a control unit having a lead-lag function with a minimum of mechanical linkages to minimize production costs, maintenance problems, backlash and other problems inherent in prior art mechanical linkages. Particularly, the unit of the present invention is a hydraulic means for generating a lead-lag function to stabilize a hydraulic servo loop. The simplicity and compactness of the unit according to the present invention overcomes many of the production and maintenance problems involved in the prior art devices. The unit of the present invention advantageously provides a transfer function in the form of K (T S l)/(T S 1) as will be explained further in the body of the specification.

The above objects and advantages are obtained with two pistons of different cross-sectional area that are biased with respect to each other. They form a first chamber with the larger piston, which chamber has an inlet and an axially spaced outlet, and a second substantially closed expansible chamber between the pistons that is provided with fluid so that axial movement of the larger piston will produce a greater axial movement of the smaller piston with the movement ratio correlated to the ratio of the piston areasJThe larger diameter piston will, by its axial position with respect to the outlet, control the effective cross-sectional area of the first expansible chamber outlet so that fluctuations in fluid flow through the inlet will correspondingly produce fluctuations in the axial position of the larger piston and correspondingly greater fluctuations in the position of the smaller piston. Bleed passages in one or more of the pistons will tend to reduce the ratio of piston movement for low frequency oscillations of fluid flow as compared to the ratio of movement between the pistons for high frequency oscillations of fluid flow.

The above control unit having a lead-lag functionvif particularly useful when the smaller piston is drivingly connected to the throttle control linkage of a prime mover having a positive displacement pump that produces a fluid flow output correlated to its speed, so that the fluid flow output may be fed to the first expansible chamber as a feed-back signal of the actual engine speed. More particularly, the abovedescribed mechanism may be employed in the environment of the power system control of the Lewis et al patent, US. Pat No. 3,324,740, which issued June 13, 1967. In such an environment, the lead-lag function device of the present invention has the advantages of fewer linkages when compared with the device providing a similar function in the Lewis et al. patent. Further, the response characteristics of the device will advantageously vary with the frequency of fluid flow input change.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects, features and advantages of the present invention will become more clear from the following detailed description when considered in connection with the accompanying drawings of a preferred embodiment of the present invention, wherein:

FIG. 1 is a somewhat schematic presentation of a power system wherein a control unit incorporating the features of the present invention is employed;

FIG. 2 is a cross-sectional view of the lead-lag function device combined with a simple throttle cam linkage, which may be used with the FIG. 1 system; and

FIG. 3 is a cross-sectional view of the lead-lag device combined with a more complex control unit, which may be employed with the FIG. 1 system.

DETAILED DESCRIPTION OF THE DRAWING Although the lead-lag function device is employed in different combinations in FIG. 2 and in FIG. 3, like numbers have been used for like parts in the various figures, since the subcombination is basically the same.

The schematic representation of FIG. 1 applies to both of the above-mentioned combinations and it is to be understood that although a preferred combination of the present invention uses the lead-lag function device with a prime mover throttle control system, the device may be used in widely differing combinations according to the broader aspects of the present invention, for example, in the controlsystem of a complex machine tool or in production line equipment.

While in this detailed description, the power system specifically relates to a motor vehicle, it should be kept in mind that the load could be in a stationary apparatus, for example, a turbine driven generator of a power station or the hydraulic motor driven carriage of a com plex machine tool. The lead-lag device may be applied to any prime mover having a motive fluid input or to any device having apower source input. For example, an electric motor may be used to drive the load and its input electrical energy may be adjusted by a rheostat instead of a carburetor in the case of an internal combustion engine.

As shown in FIG. 1, the overall power system combination includes a prime mover, for example, an internal combustion engine 11 having a drive shaft 12 drivingly connected through a change speed transmission 13 and a second drive shaft 14 to a load, for example a differential 15 having wheel shafts 16 of a driven vehicle. The control unit 17 correlates the engine speed and torque output with load and desired speed as indicated by the manually operable throttle.

The throttle 103 'may be-pivotally actuated by an operator of the vehicle for reciprocating the connection linkage 104 as .an input to the control unit 17. Further, the operator will select a desired drive, for exarnple, forward, reverse, or neutral, with the lever 105,

which signal is fed to the control unit 17 through link- 'line 109 to the transmission .13.

A feed-back speed signal is provided by a positive displacement fluid pump driven by the internal combustion engine 11 of FIG. 1 or the electric motor of the above contemplated embodiment to produce a fluid' flow in line 110 leading to the control unit 17 that varies according to prime mover speed. For control'purposes, a constant pressure fluid source may be provided by line 111 to the control unit 17.

A simplified control unit 17 is shown in FIG. 2 and employs a spool body 18 having formed therein,

preferably by boring, three coaxial and adjacent bores. A first bore 19, preferably cylindrical, extends into a second boref20, preferably cylindrical, of a substantially smaller cross-sectional area. A pistonor a spool 21 is generally in sealing engatement with the bore and is rigidly connected to a piston rod 22 that extends through the end wall of the chamber 19 with the interposition of a conventional sealing O-ring 23. Annular piston 24 freely surrounds the piston rod 22 and is in generally sealing engagement with the walls of the bore 19 to form a first annular expansible chamber 25 formed between the end wall of the bore 19 and the side of the piston 24 opposite from the piston 21. A second expansible chamber26 is annular and formed by the bores 19 and 20 between pistons 21 and 24. The collar 27 rigidly mounted on the piston rod 22 forms an abuttment surface for a compressed coil spring 28 that also abuts against the piston 24 to resiliently bias the pistons 21 and 24 away from each other. A second compressed coil spring 29 engages between the opposite end wall of the body 18 and the piston 21 toresiliently bias the piston 21 and its piston rod 22 in the right hand direction as seen in FIG. 2.

. The-fluid flow that is correlated to the speed of the prime mover and carried in previously mentioned line 110 is' fed through the inlet 30 into the chamber 25 from which chamber 25 the fluid will flow through outlet 31 to a line 32, leading to a fluid sump or other source of low pressure fluid. From FIG. 2, it is seen that piston 24, which is urged in the right hand direction by spring 28 will move to the left under the influence of pressurized fluid coming from line 110 until the outlet cam follower 35 will tend to pivot lever 36 due to the pin 37 and slot 38 connection between the two members 35, 36 of the linkage. An intermediate portion of lever 36 is pivotally connected by a pin and correspondingly shaped hole 39 to the terminal end of the piston rod 22. The opposite end of thelever 36 is pivotally connected at 40'to the previously'desc'ribed control linkage 107, which for example leads to the conventional carburetor of an internal combustion engrne.

In operation of the control unit shown in FIG. 2, the operator or i a suitable program will vertically reciprocate the control linkage 104 to a fixedpredetermined position where the relationship between the cam surface 34 and cam follower 35 is such that a desired prime mover speed has been selected. With the pistons 24 and 21 in equilibrium, pivot point 39 will be substantially stationary so that lever 36 will pivot as a first class lever to correspondingly move linkage 107 so that the carburetor will correspondingly be adjusted to the predetermined speed. It may be assumed that the load conditions are such that the device as shown is now in equilibrium.

back fluid flow in'line l 10. This increaseof flow entering chamber 25 will produce a corresponding increase influid pressure within expansible chamber 25 for-the same exposed cross-sectional area of outlet 31. As a v result, piston 24 will no longer be in equilibrium and will move to the left under theinfluence of the increased pressure on its right hand face. Due to the. in-

terposed spring 28 and the trapped quantity of fluid within the expansible chamber 26, the piston 21 will correspondingly move to the left. The movement of the piston 21 to the left will be greater than the movement of the piston 24 to the left, because of an amplification factor related to the difl'erence in effective areas of the pistons. That is, the ratio of their axial movements will be correlated to the ratio of their effective surface areas exposed to fluid within chamber 26. It is seen that the piston 21 has an effective surface area, with respect to chamber 26, that is substantially smaller than the effective surface area of piston 24 with respect to chamber 26 because of the difference in size of the bores 19 and 20. Thus, a small movement of the piston 24 to the left will produce a correlated substantially greater movement of the piston 21 and piston rod to the left. Since there has been no changein theposition- Correspondingly, if after the control unit has again reached a condition of equilibrium, an additional load is suddenly placed upon the prime mover, the engine speed will decrease correspondingly to produce a corresponding decrease in fluid flow through feed-back line 110. Thus, the flow of fluid entering expansible chamber 25 through inlet 30 will correspondingly be reduced to produce a reduction of pressure acting upon the right hand face of the piston 24. The piston 24 will no longer be in equilibrium and will move to the right under the influence of the spring 28 and pressure within expansible chamber 26. Due to the confined fluid within expansible chamber 26, the piston 21 will move to the right, but to a greater extent than the piston 24 at the above-mentioned ratio of their movement and ratio of their effective cross-sectional areas. Movement of piston 21 to the right will produce a corresponding movement of piston rod 22 to the right for pivoting lever 36 counter-clockwise about pivot pin 37 to move the carburetor control linkage 107 in the direction of increasing flow of motor fluid to the prime mover. This increase of motor fluid to the prime mover will produce a corresponding increase in engine speed, to compensate for the added load.

A particular advantage of the present invention is that the response of this system to quickly applied changes in load or changes in prime mover speed will be met with the control movement of the carburetor linkage that is correspondingly proportionately greater and quicker than would be the case with a slowly applied change in load. This difference in response is obtained by bleed passages in one or more of the pistons 21, 24. These passages may be through bores 41, 42, respectively, or great tolerances between the respective pistons and their bores 20, 19 or piston rod 22. Thus, with a high frequency change of engine speed that produces a high frequency change in pressure within the expansible chamber 25, the effect of the bleed passages 41, 42 will be negligible so that the ratio of position change between the pistons 21, 24 will be directly correlated to the difference in their respective effective cross-sectional areas exposed to expansible chamber 26. However, with low frequency fluctuations of pressure within expansible chamber 25, there will be a bleed of fluid from or to chamber 26, depending upon whether the pressure is increased or decreased within expansible chamber 25. With these lower frequency fluctuations, the effect of the bleed passages 41, 42 will be quite substantial so that the true ratio of distance travelled between the pistons 21, 24 will be proportionately less than the ratio of effective cross-sectional areas of these pistons with respect to the chamber 26.

In all of the above described operations, the area to the left of piston 21 is viewed in FIG. 2, is freely vented by means of a fluid pressure line 43 leading to the sump or under constant pressure by line 43 leading to a source of constant fluid pressure. Thus, the' spring 29 may be the only bias to the right on piston 21 or it may be replaced or combined with a constant fluid pressure bias.

In FIG. 3, the lead-lag function device of FIG. 2 has been placed in a more extensive environment of the control unit combination of the above-mentioned patent to Lewis et al., U.S. Pat. No. 3,324,740, with the corresponding structure that it has replaced being removed. For purposes of continuitywiththe above patent, the disclosure of which is incorporated herein in its entirety, the reference numerals of the lewis et al. patent have been maintained for purposes of the following description. Lead-lag device of FIG. 2 may be incorporated in its entirety in FIG. 3 with respect to elements 18-32 and 4143, although all of these elements have not been shown in the reduced scale drawing of FIG. 3. As a variation, the bleed passages 41, 42 are replaced by greater tolerances with respect to the fit between pistons 21 and 24 and their bores 20, 19, respectively, and the spring 29 is replaced by a bias provided by a constant fluid pressure source 111 (which is shown in FIG. 1) being connected to line 43.

As shown in FIG. 3, the control unit 17 comprises housing 130 into which lead: throttle input signal rod 104, drive selective control rod 106 from drive selector (shown in FIG. 1); inlet 30 to which prime mover speed feed-back signal is connected ducting fluid flow responsive to prime mover speed, and inlet 43 ducting a constant pressure fluid. Leading from the control unit is speed error signal rod 107 and drive ratio control signal rod 109.

Turning now to the internal assembly of this control unit, throttle input signal rod 104 is movable longitudinally through opening 137'in the housing with compression spring 138 located between housing and flange 139 to bias the throttle rod away from the control unit housing. This throttle control may be operated by a vehicle accelerator pedal. Attached to throttle input signal rod 104 is controlcam 140 having control cam surfaces 141 and 142. Control cam surface 141 generates, with cam follower 143, a position signal proportional to the desired speed of the prime mover. As cam follower 143 moves longitudinally, pivot pin 144 is moved together with link 145.

Also connected to link 145 by pin 154 is piston rod 22 to which is attached piston 21. Pin 154 extends through slot 157 in piston rod 22 and is biased to one end of the slot 157 -by compression spring 158 extending between the members 159 and 160, with member 159 attached for movement with piston rod 22 and member 160 rigidly carried by link 145. In this manner, link 145 and piston rod 22 move together up to a certain point, however, any subsequent movement of piston rod 22 past the limits of movement of link 145 requires compression of spring 158. The other end of lever 145 is pivotally connected to rod 167 by a lost motion joint similar to 157-160. Rod 167 is linked by pin 169 to link 168 which is pivoted about support member 170 and moves longitudinally speed error signal rod 107 pivotally attached by pin 171 to link 168.

To explain the operation of this portion of the control, assume that throttle input signal rod 104 is depressed to compress spring 138 and move control cam 140 downward. This movement of control cam 140 moves cam follower 143 to the left by virtue of its contact with cam surface 141. Concurrently, a constant pressure fluid input is supplied through inlet 43 tending to move piston 21' to'the right while positive displacement pump driven by the prime mover is supplying fluid flow through inlet 110 tending to move piston 24 to the left. As cam follower 143 moves to the left, it pivots link 145 about pin 154 (since movement of pin speed rises to increase the flow within the chamber 25 by action of the fluid supplied by the positive displacement pump driven by the prime mover; this flow increase will cause piston 24 to move to the left until the forceson each face of the piston exerted by the springs and fluid are again equal. At this time, in accordance with the piston of cam follower 143, an equilibrium will be reachedbetween port 31, the control fluid pressure within chamber 25, and the positioning of the various linkages including speed error signal rod 107, to regulate the desired prime mover speed called for by the power setting of throttle input signal rod 104.

It will be noted that when piston 24 moves to the right it will close port 31 thereby lessening the flow through port 31. In this manner a negative feed-back is supplied within the control linkages to damp the action 110 toallow piston 24 to move to the right. This action will cause piston 21 and its carried rod 22 to correspondingly move to the right for movement, through theconnecting linkage, of thespeed error signal rod 107 to the left to increase the motive fluid flow to the prime mover and therefore with no further action on the part of the operator, the increased load will be powered at the required speed called for by the accelerator position by automatically regulating the motive fluid flow to the prime mover. Now assuming that the load is increased with no change in power setting, the pistons will move to the right until the pressures within the expansible chambers equalize with the spring forces to maintain speedor continued movement to the right will cause piston rod 22 to contact the override rod 191, for change inthedrive ratio as more fully described in the Lewis et al. patent.-

If the load is thereafter decreased, thepiston 24, piston 21 and piston-rod 22 will move to the left due to engine racing to correspondingly, through the connecting linkage, move the rod107 in a direction to decrease of the control unitand prevent over compensation of 25 the control.

For idle speed control, rod 167 is fastened by pin 166 to move with member164. Compression spring 173 extends between a rod flange member 164 to bias pin 166 and member 164 to one end 'of slot 172 such that generally member 164 and rod 167 move in unison;

' drive ratio control actuator of the power transmission byv actuating" drive ratio control signal rod 109 will not be described specifically, since reference may be made to the Lewis et al patent and the same is not necessary for. the understanding of the lead-lag unit operation. It will suffice to say that cam follower 175 will contact cam surface 142 of cam 140 for operation of the transmission according to the selection of forward, reverse, or neutr made with linkage 106 for moving control link 109. When full throttle operation cannot restore engine speed with a suddenly applied heavy load, over travel of rod 22 by distance 210 will downshift the transmission by engaging rod 191. Also, lever 208 that is connected by pin 213 and linkage 212 to the throttle linkage will correlate throttle and transmission control.

For a description of the operation of the lead-lag device of FIG. 3, it will be assumed that the operator has reached a desired drive speed, so that the motive fluid regulator portion of the control unit 17 through the balancing of the pressure on each side of pistons 21, 2 4, regulates the prime mover to its lowest possible power to maintain that speed called for by the power setting of the accelerator or throttle 103. When a greater load is impressed on the power system by the driven unit, the immediate reaction within the power system is to decrease the prime mover speed due to the greater load. Because of this, the prime mover speed pump will slow decreasing the pressure supplied by line the supply of motor fluid to the prime mover for correspondingly reducingactual. engine speed to approximately the desired speed value as set by the operator linkage 104. f

Within the confines of the above-described basic operation, there will be the additional variable operation in accordance with the frequency of load fluctuation or the rapidity of load-increase or-load decrease. With high frequency of load fluctuation or a single rapid change in impressed load, there will be no appreciable leakage through leakage passages 41, 42 so that the maximum ratio movement between pistons 21 and 24 will be in effect to produce a correspondingly quick and maximum movement of the motorfluid con-' trol rod 107, which maximum movement will automatically subside with leakage in passages 41 and 42. With low frequency fluctuations in the load or a single'slow change in load, leakage through the passages 41, 42 will come into play to a greater extent to minimize the 9 35 32 B me it a '1' It? a li zmi llf A effective cross-sectional area of the right hand face of piston 24 in FIG. 2.

A effective cross-sectional area of the left hand face of piston 24 in FIG. 2.

A effective cross-sectional area of right hand face of piston 21, in FIG. 2.

k the gradient for spring 29 k the gradient for spring 28 q the pressure-flow gradient of the passage 42 q the pressure-flow gradient of the passage 41 x the translational movement of piston rod 22 Q the fluid flow from line 1 While several variations of a single preferred embodiment have been described in detail and are highly advantageous in their own right, further modifications, embodiments and variations are contemplated for example as set forth throughout the description, according to the broader aspects of the present invention, which is to be defined within the spirit and scope of the attached claims.

What is claimed as new and desired to be secured by Letters Patent in the United States is:

1. A control unit for a power unit having an output with a speed characteristic, means for producing a feed-back fluid flow correlated to the speed of the power unit and an input power control, comprising: a relatively stationary valve body having a first fluid chamber of one substantially uniform cross-sectional area opening into a second fluid chamber of a second smaller substantially uniform cross-sectional area; a first piston generally sealingly mounted within said first chamber to form a first expansible chamber on one side of said first piston; a second piston generally sealingly mounted within said second chamber and forming a second expansible chamber with the other side of said first piston; means drivingly interconnecting said first and second pistons for relative axial movement and for movement of said second piston in response to movement of said first piston; a fluid inlet opening into said first expansible chamber for conducting feed-back fluid; a fluid outlet from said first expansible chamber axially spaced from said fluid inlet opening; a control member selectively positionable according to desired speed; means for interconnecting said control member and said second piston with the input power control for changing the quantity of power fed to the power unit according to the positioning of said control member and according to the positioning of said second piston, whereby feed-back fluid from the power unit that is correlated in flow to the speed of the power unit will pressurize said first chamber in an amount correlated to the position of said first piston relative to said outlet for correspondingly moving said second piston and therewith the input power control through said interconnecting means.

2. The device of claim 1, wherein said means interconnecting said pistons includes a spring.

3. The device of claim 1, wherein said means interconnecting said pistons includes fluid generally con fined in said second expansible chamber so that axial movement of said first piston will tend to produce a correspondingly greater axial movement of said second piston correlated to the ratio of effective cross-sectional areas of said pistons exposed to said second expansible chamber.

includes through fluid bleed passage means so that the relative movement between pistons will be greater for high frequency oscillations of said first piston than it will be for low frequency oscillations of said first piston. 6. The device of claim 1, including means biasing said second piston relative to said body toward said first piston.

7. The device of claim 1, wherein said means for interconnecting said second piston and saidcontrol member with the input power control includes a lever having three spaced pivot points, with one of said pivot points drivingly connected to said control member, a second pivot point drivingly connected to said second piston and a third pivot point to be drivingly connected to the input power control.

8. The device of claim 7, wherein said control member is a cam, and said lever is freely mounted only by said pivot points.

9. The device of claim 1, including a piston rod axially extending from said second piston through said first chamber and forming a part of said means for interconnecting said control member, said second piston and the input power control; said first piston being annular and surrounding said piston rod.

10. A hydromechanical lead-lag control device, for use in a power system having. speed related fluid flow and a mechanical position device representing other system parameters, comprising:

a. a first cylinder containing a partially restrained free piston having opposite first and second head faces each exposed to a different one of two cylinder volume spaces and fluid supply and exhaust ports in one said cylinder space for supply to and passage through said cylinder of speed related fluid flow, said ports beingso located as'toperrnit said free piston to close said exhaust port without closing said supply port; said first cylinder and free piston combination having fluid 'bleed passage means between said two cylinder faces topermit slow equalization of pressures;

b. a second cylinder separated into a work volume space and a free space by a drive piston; an actuating rod fixed to said drive piston, said rod having remote means for attachment to a mechanical position device; said second cylinder having fluid conduit means communicating between its work volume space and the second cylinder space of said first cylinder and having port means for draining fluid from its free space; said drive piston also having mechanical biasing means for forcing said drive piston and actuating rod in a direction toward said work volume space; said second cylinder and drive piston combination having fluid bleed passage means between said work volume space and said free spring; and

. additional meachnical biasing means partially restraining said free piston by exerting equal force on the two said pistons, biasing said free piston toward said supply and exhaust ports and biasing said drive piston away from said work volume space whereby said control device will move said actuating rod more I or less precipitously in response to sudden or large scale variations of speed as measured by fluid flow and relatively little in response to other variations in predetermined relationships as determined by the ratios among the piston face areas and biasing means forces.

1 1. A hydromechanical lead lag control device, for a power system wherein speed is represented by a fluid flow rate and other parameters by mechanical position, comprising a primary cylinder with a piston substantially responsive to sudden or large scale variations of fluid flow rate but non-responsive to flow rate variations below a predetermined level;' a secondary tachment to said system mechanical position; said pistons being mechanically biased in oppositiontoincreased fluid flow with said secondary piston being biased for movement relative to said cylinders'and the primary piston beingbiased for movement relativeto the secondary piston whereby a mechanicalpositioning device in a system may be moved quickly to adjust other parameters to compensate for precipitous. changes in speed but ignore minor deviations or gradual speed changes in accordance with criteria built into the control device. g

* l t I! Pat nt 3.685.501 Dated August 22, 1972 In Thomas S. Honda It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 10, column 10, line 64, delete "spring" and insert space Signed and sealed this 9th day of January 1973;

(SEAL) Attest:

ROBERT GOTTSCHALK R. EDWARD M.FLETCHER,J Commissioner f Patents Attesting Officer FORM Po-1o50 (10-69) USCOMM-DC 60376-P69 Q U.5. GOVERNMENT PRINTING OFFICE I I969 O355-334 

1. A control unit for a power unit having an output with a speed characteristic, means for producing a feed-back fluid flow correlated to the speed of the power unit and an input power control, comprising: a relatively stationary valve body having a first fluid chamber of one substantially uniform cross-sectional area opening into a second fluid chamber of a second smaller substantially uniform cross-sectional area; a first piston generally sealingly mounted within said first chamber to form a first expansible chamber on one side of said first piston; a second piston generally sealingly mounted within said second chamber and forming a second expansible chamber with the other side of said first piston; means drivingly interconnecting said first and second pistons for relative axial movement and for movement of said second piston in response to movement of said first piston; a fluid inlet opening into said first expansible chamber for conducting feed-back fluid; a fluid outlet from said first expansible chamber axially spaced from said fluid inlet opening; a control member selectively positionable according to desired speed; means for interconnecting said control member and said second piston with the input power control for changing the quantity of power fed to the power unit according to the positioning of said control member and according to the positioning of said second piston, whereby feed-back fluid from the power unit that is correlated in flow to the speed of the power unit will pressurize said first chamber in an amount correlated to the position of said first piston relative to said outlet for correspondingly moving said second piston and therewith the input power control through said interconnecting means.
 2. The device of claim 1, wherein said means interconnecting said pistons includes a spring.
 3. The device of claim 1, wherein said means interconnecting said pistons includes fluid generally confined in said second expansible chamber so that axial movement of said first piston will tend to produce a correspondingly greater axial movement of said second piston correlated to the ratio of effective cross-sectional areas of said pistons exposed to said second expansible chamber.
 4. The device of claim 3, wherein one of said pistons includes fluid bleed passage means there-through so that the relative movement between pistons will be greater for high frequency oscillations of said first piston than it will be for low frequency oscillations of said first piston.
 5. The device of claim 3, wherein each of said pistons includes through fluid bleed passage means so that tHe relative movement between pistons will be greater for high frequency oscillations of said first piston than it will be for low frequency oscillations of said first piston.
 6. The device of claim 1, including means biasing said second piston relative to said body toward said first piston.
 7. The device of claim 1, wherein said means for interconnecting said second piston and said control member with the input power control includes a lever having three spaced pivot points, with one of said pivot points drivingly connected to said control member, a second pivot point drivingly connected to said second piston and a third pivot point to be drivingly connected to the input power control.
 8. The device of claim 7, wherein said control member is a cam, and said lever is freely mounted only by said pivot points.
 9. The device of claim 1, including a piston rod axially extending from said second piston through said first chamber and forming a part of said means for interconnecting said control member, said second piston and the input power control; said first piston being annular and surrounding said piston rod.
 10. A hydromechanical lead-lag control device, for use in a power system having speed related fluid flow and a mechanical position device representing other system parameters, comprising: a. a first cylinder containing a partially restrained free piston having opposite first and second head faces each exposed to a different one of two cylinder volume spaces and fluid supply and exhaust ports in one said cylinder space for supply to and passage through said cylinder of speed related fluid flow, said ports being so located as to permit said free piston to close said exhaust port without closing said supply port; said first cylinder and free piston combination having fluid bleed passage means between said two cylinder faces to permit slow equalization of pressures; b. a second cylinder separated into a work volume space and a free space by a drive piston; an actuating rod fixed to said drive piston, said rod having remote means for attachment to a mechanical position device; said second cylinder having fluid conduit means communicating between its work volume space and the second cylinder space of said first cylinder and having port means for draining fluid from its free space; said drive piston also having mechanical biasing means for forcing said drive piston and actuating rod in a direction toward said work volume space; said second cylinder and drive piston combination having fluid bleed passage means between said work volume space and said free spring; and c. additional meachnical biasing means partially restraining said free piston by exerting equal force on the two said pistons, biasing said free piston toward said supply and exhaust ports and biasing said drive piston away from said work volume space whereby said control device will move said actuating rod more or less precipitously in response to sudden or large scale variations of speed as measured by fluid flow and relatively little in response to other variations in predetermined relationships as determined by the ratios among the piston face areas and biasing means forces.
 11. A hydromechanical lead-lag control device, for a power system wherein speed is represented by a fluid flow rate and other parameters by mechanical position, comprising a primary cylinder with a piston substantially responsive to sudden or large scale variations of fluid flow rate but non-responsive to flow rate variations below a predetermined level; a secondary cylinder with a piston similarly responsive to hydraulic parameters and regeneratively responsive to movements of said first piston; an actuating rod fixed to said second piston and having connecting means for attachment to said system mechanical position; said pistons being mechanically biased in opposition to increased fluid flow with said secondary piston being biased for movement relative to said cylinders and the primary piston being biased for Movement relative to the secondary piston whereby a mechanical positioning device in a system may be moved quickly to adjust other parameters to compensate for precipitous changes in speed but ignore minor deviations or gradual speed changes in accordance with criteria built into the control device. 